The recently introduced twisted and coiled polymer muscle is an inexpensive and lightweight compliant actuator. Incorporation of themuscle in applications that rely on feedback creates the need for deflection and force sensing. In this paper, we explore a sensing principle that does not require any bulky or expensive additional hardware: Self-sensing via electrical impedance. To this end, we characterize the relation between electrical impedance on the one hand, and deflection, force, and temperature on the other hand for the Joule-heated version of this muscle. Investigation of the theoretical relations provides potential fit functions that are verified experimentally. Using these fit functions results in an average estimation error of 0.8%, 7.6%, and 0.5%, respectively, for estimating deflection, force, and temperature. This indicates the suitability of this self-sensing principle in the Joule-heated twisted and coiled polymer muscle.